Retinitis Pigmentosa

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Often diagnosed in childhood or adolescence, retinitis pigmentosa (RP) is an inherited retinal disease causing progressive loss of night and peripheral vision. The condition often leads to legal and sometimes complete blindness.

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What is Retinitis Pigmentosa?

Retinitis pigmentosa, also known as RP, refers to a group of inherited diseases causing retinal degeneration and a decline in vision. The retina is a thin piece of tissue lining the back of the eye. Rod and cone photoreceptors in the retina convert light into electrical signals that the brain interprets as vision. People with RP experience a gradual decline in their vision, because photoreceptors degenerate.

Forms of RP and related diseases include Usher syndrome, Leber congenital amaurosis, and Bardet-Biedl syndrome, among others.

What Is Retinitis Pigmentosa (RP)?

Symptoms

Symptoms depend on whether rods or cones are initially involved. In most forms of RP, rods are affected first. Because rods are concentrated in the outer portions of the retina and are activated by dim light, their degeneration affects peripheral and night vision. Vision becomes more constricted over time. If and when the disease progresses and cones become affected, visual acuity, color perception, and central vision are diminished.

Night blindness is one of the earliest and most frequent symptoms of RP. People with mainly cone degeneration, however, first experience decreased central vision and reduced ability to discriminate colors and perceive details.

RP is typically diagnosed in children, adolescents and young adults. It is a progressive disorder. The rate of progression and degree of visual loss varies from person to person. Many people with RP are legally blind by age 40, with a central visual field of less than 20 degrees in diameter.

Inheritance

An estimated 100,000 people in the U.S. have RP, mainly caused by mutations (variations) in a single gene inherited from one or both parents. The mutated gene gives the wrong instructions to photoreceptor cells, telling them to make an incorrect protein or too little or too much protein. (Cells need the proper amount of particular proteins in order to function properly.) Mutations in dozens of genes have been linked to RP.

Genetic mutations can be passed from parent to offspring through one of three genetic inheritance patterns — autosomal recessive, autosomal dominant, or X-linked.

In autosomal recessive RP, both parents carry one copy of the mutated gene and one normal copy, but have no symptoms themselves. They are therefore referred to as unaffected carriers. Each of their children has a 25 percent chance of being affected by inheriting a mutated copy from each parent. If the child inherits one mutated copy from one parent, they will be an unaffected carrier.

In autosomal dominant RP, usually one parent is affected and is the only parent with a mutated copy of the gene. A child has a 50 percent chance of being affected through the inheritance of the mutated copy from. The unaffected parent genetics doesn’t play a known role in the inheritance of the disease.

In X-linked RP, the mutated gene for the disease is located on the X chromosome. Females have two X chromosomes and can carry the disease gene on one of their X chromosomes. Because they have a healthy version of the gene on their other X chromosome, carrier females are less frequently affected by X-linked diseases. Males have only one X chromosome (paired with one Y chromosome) and are therefore genetically susceptible to X-linked diseases. Males with X-linked diseases pass their Y chromosome to their sons, and therefore will never pass an X-linked disease to their sons. Female carriers have a 50 percent chance (or 1 chance in 2) of passing the X-linked disease gene to their daughters, who become carriers, and a 50 percent chance of passing the gene to their sons, who are then affected by the disease.

If a family member is diagnosed with RP, it is often advised that other members of the family also have an eye exam by a physician who is specially trained to detect and treat retinal degenerative disorders. Genetic counselors are excellent resources for discussing inheritability, family planning, genetic testing, and other related issues.

The most common genes associated with retinitis pigmentosa are PRPF31, PRPH2, RDH12, RHO, RPE65, ABCA4, MAK, MERTK, NR2E3, PDE6B, and RPGR.

Living with the Disease

There are many services and accommodative and assistive resources available to people and families with RP. Visit the Foundation’s Low Vision Resources page to learn about many of these resources. A low vision specialist can help recommend the resources that are right for you.

More information on managing RP is in the Newly Diagnosed section of this Web site.

Genetic Testing

Genetic testing is available for RP. It helps assess the risk of passing the disorder from parent to offspring. It also helps with attaining an accurate diagnosis. A patient with an accurate diagnosis is in a better position to understand which emerging treatment approaches and clinical trials are most appropriate for them.

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